Final answer:
A proprioceptor known as a muscle spindle detects muscle stretch and triggers a stretch reflex to contract the muscle, preventing damage and maintaining muscle tone.
Step-by-step explanation:
A proprioceptor that detects passive stretch of a muscle, triggering a stretch reflex. This proprioceptor is known as a muscle spindle, which is a stretch receptor within the muscle that detects changes in muscle length. Upon activation by stretch, the muscle spindle induces a reflexive contraction in the muscle to maintain constant muscle length and prevent damage such as overstretching or tearing.
The muscle spindle is significant for maintaining muscle tone and posture, and it plays a critical role in the proprioceptive system, providing feedback to the central nervous system about the position and movement of the body part. A related structure is the Golgi tendon organ, which senses changes in muscle tension and helps to prevent muscle damage from excessive force by causing relaxation.